Werribee system

The Werribee River flows south-east from the Wombat State Forest near Ballan before dropping through the Werribee Gorge to Bacchus Marsh and then flowing into Port Phillip Bay at Werribee. The Lerderderg River is a major tributary that joins the river at Bacchus Marsh. The main storages in the Werribee system are Pykes Creek Reservoir, Melton Reservoir and Merrimu Reservoir.

The Werribee River and its tributaries continue to be a place of significance for Traditional Owners and their Nations. The Registered Aboriginal Parties (RAPs) in the Werribee River area are the Wathaurung Aboriginal Corporation (on the western side of the Werribee River) and the Wurundjeri Land and Compensation Cultural Heritage Council Aboriginal Corporation (on the eastern side of the river in the upper catchment).

Environmental values

The Werribee system supports a range of native fish including river blackfish, flathead gudgeon, short-finned eel, tupong, Australian smelt, several species of galaxiids, and a large population of black bream in the estuary. A highly diverse community of frogs and waterbugs inhabit the upper reaches and platypus are present in the lower reaches. The freshwater-saltwater interface of the Werribee River estuary is a regionally significant ecosystem due to the many aquatic plants and animals it supports, providing nursery habitat for juvenile freshwater fish species and estuarine species such as black bream.

Social and economic values

The Werribee River is a resource for agriculture, industry, recreation and tourism. The system provides irrigation water for agricultural industries throughout the Bacchus Marsh and Werribee areas (including the Werribee market gardens) and domestic water for Melton and Bacchus Marsh.

The Werribee River and its tributary the Lerderderg River support popular camping and hiking spots in the Wombat State Forest and Lerderderg State Park. Along its length, the Werribee River provides opportunities for recreational activities including fishing, birdwatching, canoeing, kayaking and bushwalking.

In the lower reaches, the river meanders through the Werribee River Park and Werribee Park Tourism Precinct (which includes the Open Range Zoo, National Equestrian Centre, Shadowfax Winery, Mansion Hotel and Spa, Western Treatment Plant, Refectory and Golf Club) which attracts more than a million visitors a year to the region. The Werribee River Trail and Federation Trail bike paths are popular recreational cycling routes.

Conditions 2018

After a wet 2016–17, winter 2017 was one of the driest winters on record for the Werribee system. Drier conditions prevailed across the catchment with below-average rainfall and higher-than-average temperatures in spring, summer and autumn 2017–18. Small volumes of water for the environment were delivered to protect and maintain current ecological objectives in the Werribee system.

Water for the environment was delivered into Pyrites Creek (reach 6) from Lake Merrimu in spring 2017. High flows were delivered at the beginning of October 2017 and flows were reharvested in Melton Reservoir for later use. A second fresh in November 2017 was passed through Melton Reservoir to meet flow objectives in the lower Werribee River. These flows flushed organic matter from benches and supported the recruitment and growth of native vegetation along the creek. No water for the environment was released from Lake Merrimu to Pyrites Creek in summer/autumn, as a wet winter/spring followed by a dry (cease-to-flow) summer/autumn is the natural cycle of this creek.

Flows in the lower Werribee River in 2017–18 were low all year, except for a few freshes that resulted from storms in spring/summer. The fresh delivered to Pyrites Creek in November 2017, combined with water held in storage — reharvested flows from Pyrites Creek low flows and the October fresh — was released from Melton Reservoir to deliver a large fresh to the lower Werribee River. Water for the environment was delivered in the lower Werribee River in autumn 2017, to maintain water quality and support native fish habitat and recruitment. Monitoring in the last two years in the lower Werribee River has detected a higher catch rate of young-of-year galaxiid species following high freshes in November 2016 and November 2017. These flows provide suitable conditions for diadromous native fish to complete their lifecycles — to disperse and breed — in southern Victoria's coastal rivers.

Another exciting discovery in the lower Werribee River was the presence of a young-of-year Australian grayling caught in November 2016 and an another, older one, caught in autumn 2017. These represent the first and second records of Australian grayling in the Werribee River system, and it is likely due to improved fish passage in the Werribee River thanks to recently constructed fishways and managed flows.

Scope of environmental watering

Table 1
Potential environmental watering actions and objectives for the Werribee system

Potential
environmental watering

Environmental objectives

Pyrites Creek
(reach 6)

Spring/summer freshes (up to 3 freshes of 30 ML/day for 2 days in September–December)

Improve waterbug habitat by scouring silt and sand from riffles

Promote vegetation growth

Spring/summer high flows (up to 3 high flows of 130 ML/day for 2 days in September– December)

Provide flows to allow native diadromous fish to move between the freshwater river and saltwater estuary to complete their life cycle

Provide habitat for waterbugs and native fish, and support plant growth in reach 9

Summer/autumn/winter freshes (up to 3 freshes of 80 ML/day2 for 2 days during January–May)

Maintain pool water quality for fish and platypus in reach 9

Increase the recruitment of juvenile black bream in the estuary

Scour silt and algae from riffles in reach 8

Winter/spring/summer freshes (up to 4 freshes of 350 ML/day for 3 days during June– December)

Increase the diversity of riparian vegetation in reaches 8 and 9

Provide fish movement cues (all)

Inundate saltmarsh vegetation with brackish water in the estuary

1 The original recommendation from the flow study (Ecological Associates 2005, Jacobs 2014) is for 89 ML per day for four days throughout autumn. Construction of a fishway has reduced the required flow rate. This is usually the last watering action in a year, so duration is matched to remaining available water in Melton Reservoir.

2 Original recommendation from the flow study (Ecological Associates 2005, Jacobs 2014) is for 137 ML delivered in one day. The recommendation has been revised due to operational constraints to be 160 ML delivered over two days. Monitoring has shown that this achieves the hydraulic and water quality objective.

Risk management

In preparing its seasonal watering proposal, Melbourne
Water considered and assessed the risks of environmental
watering and identified mitigation strategies. Program
partners continually reassess risks and mitigation actions
throughout the water year.

Engagement

Table 2 shows the partners, stakeholder organisations and individuals with which Melbourne Water engaged when preparing the Werribee system seasonal watering proposal.

Seasonal watering proposals are informed by longer-term regional catchment strategies, regional waterway strategies, environmental flow studies, water management plans and other studies. These incorporate a range of environmental, cultural, social and economic perspectives and longerterm integrated catchment and waterway management objectives. For further details, refer to the Port Phillip and Western Port Regional Catchment Strategy and Melbourne Water's Healthy Waterways Strategy.

Werribee River Community Advisory Group including representatives of Melton and Wyndham councils, Werribee Riverkeeper, Werribee South Fishing Club, Werribee and District Anglers Club, Western Water, Port Phillip and Westernport CMA